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I I INVENroR I2] Ilo By HIS TTORNEz/s HARR/5,K/ECH, FOSTER @HQ/Qms United States Patent@ FURNACE ASSEMBLIES AND CONIBlNATION OF SUCH FURNACES Clarence J. Coberly, San Marino, Calif., assignor to Wulff Process Company, Huntington Park, Calif., a corporation of California Filed Ian. 10, 1955, Ser. No. 480,794

4 Claims. (Cl. 2'3-277) The inventions claimed herein may be briefly summaryized as embodied in a new and useful furnace having at least two regenerative masses which is operated in such a manner as to produce desired hydrocarbons from suitble hydrocarbons with a high heat economy and with a maximum possible yield of the desired hydrocarbon.

These inventions are further embodied in an assembly of two such furnaces with auxiliary apparatus, this assembly having a high heat economy and efficiency. In these furnaces the heat needed to produce certain desired reacions is supplied by contact of the suitable hydrocarbon with surfaces of the highly heated regenerative masses during a make step, these masses being heated by products of combustion during a heat period.

In any interpretation of the claims, the following denitions should apply.

The term regenerative mass, as used herein, is limited to and defined as a mass of material capable of resisting material damage at temperatures in excess of 2000 F. and which has small channels through which gases are passed in the operation of the apparatus hereinafter described.

The Word pyrolysis is used in its dictionary meaning as a chemical decomposition by the action of heat. The word crackingj is used herein to denote a pyrolysis of hydrocarbons which is not carried to the point of decomposing the hydrocarbons to carbon and hydrogen, but

yone in which new compounds are formed and hydrogen i is released.

The hyphenated Word in-gas, as used herein, is limited to and defined as the gas which enters a furnace where it is subjected to pyrolysis and which is a suitable hydrocarbon, or which contains a substantial amount of Va suitable hydrocarbon.

The 4words substantial amount are used herein to denote the percentage of a designated gas contained in a mixed gas and are limited to a percentage of more than two percent by volume of the designated gas.

The words suitable hydrocarbon, as used herein, denote any hydrocarbon which is stated in the art to be, or which is, capable of producing an off-gas containing a desired hydrocarbon by pyrolysis of said in-gas. Natural gas, or the vapors of natural gasoline, olf-gases from refineries or coking plants, and gas mixtures containing a substantial proportion of methane, ethane, propane, butane or the like are all suitable in-gases.

The hyphenated word off-gas is used herein to designate a mixed gas which has been subjected to pyrolysis in the apparatus hereinafter described and which contains a substantial amount of a desired hydrocarbon.

The words desired hydrocarbon are used herein to denote any hydrocarbon which can be produced in the apparatus by the pyrolysis of a suitable hydrocarbon.v

The apparatus described hereinafter was designed and is .well adapted to produce an olf-gas containing a substan- .'.Inow contemplate for. use of the invention. I do not Fig. I is a plan view of a new and novel furnaceV embodying my invention, the upper portion being broken away as indicated by the line I-I in Fig. II, to better illustrate the internal structure. l Y n Fig. II is a central elevational section of the furnaceA shown .in Fig. I, this section being on a plane indicated by the line II-II in Fig. I.

Figs. III, IVand V are' cross sections of the furnace.;l shown in Figs. I andII, these sections being on planesj indicated by the lines III-III, IV-IV and V-V in; Fig. II. 'Y j Fig. VI is an elevation of a two-nozzle fuel gas mani,-r fold. One of these manifolds is placed on one side of aV furnace and a three-nozzle manifold, not shown, is placed on the other side of the furnace. e

Fig. VII is a section on a plane defined by the line VII-VII of Fig. VI.

Fig; VIII is an elevation showing oneside of the fuel manifold shown in Fig. VI, this View being partlyv in' section on a plane defined by the line VIII--VIII 'of Fig. VI. l

Fig. IX is a section of the same manifold, the View being in section on a plane dened by the line-IXIX of Fig. VIII. 1

Fig. X is a side view of a portion of one of thefurnaces shown in Fig. I which shows the fuel manifolds. and fuel supply piping.

Fig. XI is a plan View of the apparatus shown in Fig. X. The fuel manifolds and piping therefor are rather complicated and are wholly or partially omitted in some gures. f

Fig. XII is a plan view of an assembly of two furnace similar to the furnace previously described showing some of the valves, piping and other auxiliaries.

Fig. XIII is an elevation of the apparatus shown in Fig. XII. 1

Fig. XIV is a diagrammatic sketch showing some of the apparatus used in the furnace assembly.

In the succeeding figures, which show separate steps in the method of operation, only those parts of the appara: tus which -are used in any step are shown in the .ligure disclosing said step. L

Fig. XV is a diagrammatic sketch showing how. .the apparatus is used to .preheat the furnaces or to keep them hot when they are not inactive use. n

Figs. XVI, XVII, XVIII and XIX are diagrammatic.L views each showing how the apparatus is operated in one of the four Acyclic steps A,.B, C and D, as hereinafter described.

Figs. XX, XXI, XXII and XXIII show the distribution of temperature in the mixing zone with diierent distribution of flow from theheating system.

Fig. XXIV is ra diagram showing fthe apparatus needed when using a liquid hydrocarbon (or oil) as a suitable hydrocarbon.

v Fig. XXV is a central section of the mixer on a plane represented by the line XXV-XXV in Fig. XXVI; j.. Fig. XXVI is a section of the mixer on a planelrepresented by the lline XXVI- XXVI in Fig. XXV.

` The complete apparatus, as diagrammatically indicated in Fig. XIV, consists of two furnaces 1 and 2 which are duplicates. Furnace 1 has a fuel supply :system S'and furnace 2 has a fuel supply system 4. Connected tothe `furnaces 1 and 2 yare four four-way valves 5, 6, 7 and 8. The apparatus also includes an off-gas pump 9 and products of combustion gas pump 10 which delivers such -flue Patented Oct. 18, 1960 gas to a stack or chimney 11. Each furnace has a burner 12 supplied with air from a pipe 13 and fuel gas under the pressure from a pipe 14, and mixed gas may be passed through an opening in the cover into the center combustion chamber of the furnace. Each end of each furnace has a small stack pipe 15 having a valve 16. The pipes 15 and valves 16 are used only in a preheating or standby step in the process, hot gases being used in the cyclic operation of the apparatus, and they are shown only in Figs. I, XIV and XV.

The furnaces, as shown in Figs. I and Il, consist of a steel shell 21 which is made in the form of an open box 21 with a flanged top upon which .a cover 22 is bolted, the assembled box with its cover being made of suficiently heavy steel to withstand a full vacuum. The cover is suiciently tight to insure such a vacuum being maintained in the shell 21 with the cover 22 in place. In the larger furnace, a small cover 23 closes a manhole in the center of the cover 22. See Figs. I and II.

Projecting beyond each end of each of the furnaces 1 and 2 is an extension 30. The inside of the box 21 is lined with a heat resisting lining 31 forming a trough and regenerative masses 32, 33, 34, 35, 36 and 37 are produced by stacking up tiles in the trough, as shown in Figs. IV, III and II. These tiles may be similar to the tile shown in Patent No. 2,473,427, patented June 14, 1949, to R. L. Hasche, the tile being, however, laid at so that horizontal ducts are formed extending along the major axis, indicated by the lines IV-I of Fig. II and II-II of Fig. I. The ducts provide channels having open paths through the masses 32-37, inclusive, from the extension 30 on one end, to an extension 30 on the other end of the furnace. After the tiles are laid, a heat resisting top lining 38 is laid and the cover 22 is bolted in place. Each of the extensions 30 is provided with distribution plates 40, as shown in Figs. I, II and V, and each of the plates is provided with small holes. These holes should be of a size to cause a pressure drop through one set of distribution plates 40 of about four inches of water when the gas ow is normal. If this pressure drop is maintained, the distribution of low of gases through the channels of the regenerative mass will be quite uniform.

The primary requirement of the regenerative masses 32 to 37 inclusive is to provide a large heat storage mass and good heat transfer between the gas and the mass. This means that the area of the passages should be as small as possible without causing an excessive pressure drop when gas is flowing through the mass at the maximum rate. It has been found that this condition is satisfied when the area of the passages is approximately 25% of the gross cross section of the mass.

The gross cross section required for a given capacity should be about .048 sq. ft. per cu. ft. of propane fed per min., or .080 sq. ft. per cu. ft. of acetylene produced p er min. with twin furnaces in which the ow is contlnuous. With masses of the proportions given above, the open passage through the masses should be about .O11 sq. ft. per cu. ft. of propane fed or about .O19 sq. ft. per cu. ft. of acetylene produced.

With masses of the above proportions and with a length which will limit the exit temperature to a value slightly above the temperature at which tars start to deposit in the channels, the maximum pressure drop through the furnace and the associated piping should be about 11/21 Hg on the heat cycle and 1" Hg on the cracking cyc e.

The regenerative tiles are stacked in the channel provided between the insulating side walls of the furnace. Half length tiles are provided to permit staggering the joints and prevent any accumulated error in the alignment of the passages. No cement is used as it has been found that the tiles will not be displaced in operation when they are installed in this manner which makes it easy to install or replace tiles and they may be removed without damage to the tiles. i

The material which has been found suitable for regenerative masses is high purity Alundum (over 99% A1203) or silicon carbide, or other highly stable high temperature ceramics. High purity Alundum is the preferred material as it has been found to be very stable at the required operating temperatures of 800 C. to 1500 C. and the heated surface of this material promotes the production of acetylene. It is `not known whether or not Alundum has a catalytic effect but it has been found to operate in this apparatus at lower temperatures than those reported in the art.

It has been found that Alundum brick of approximately the same composition as the masses should be used adjacent to the masses in that part of the furnace in which the temperature is over 800 C. This extends each way from the middle of the furnace with the furnace arrangement shown in Figs. I and II.

The various regenerative masses may be divided in various ways. It is desirable to have at least two central masses like 34 and 3S, thus leaving a central combustion space 41 into which the burner 12 may feed a combustible mixture during the heating period and to keep the furnace hot during shutdowns. During the preheating period, -as shown in Fig. XV, the pumps 9 and 10 are shut down, the valves 16 are open and air and fuel gas are supplied to the burners 12 through the pipes 13 and 14, and combustion flue gases are vented through the valves 16. When the cold furnace is heated to a temperature of about l500 F. the valves 16 are closed and the supply of air and fuel is shut off to the burners 12. During the cyclic operation the burners 12 are inactive and sealed to the admission of air or fuel so that a vacuum may be maintained in the system.

The masses 33 and 36 are optional so that there may be only two intermediate masses 34 and 35 between the masses 32 and 37. In the arrangement of regenerative masses shown in Fig. II an intermediate space 50 is shown at each end of the central portion, one adjacent to the inner face of the mass 37 and the other adjacent to the inner -f-ace of the mass 32. Two spaces 51 are also provided as shown. Each of the spaces 5) and 51 is fed with fuel through a fuel supply system such as that shown in Figs. X and XI through manifolds shown in Figs. VI, VII, VIII and IX. Referring to these figures, each manifold consists of a casting having a channel 60 fed by a fuel pipe 61 and a water channel 62 fed with circulating water which enters the channel 62 through a pipe 63 and leaves the channel 62 through a pipe 64. Each space 50 and 51 is fed by five nozzles, three on one side and two on the other, the two nozzles on one side being horizontally disposed so that they inject a stream of fuel between the streams from the three nozzles on the other side of the furnace. This provides a very uniform mixing and combustion with the hot air fed into the spaces 50 and 51, as will later be more fully explained.

Each manifold contains two or three nozzle members 65, as shown in Figs. VIII and IX. The gas emerges from the inner end of each nozzle as a relatively high speed jet from a constricted orifice 66. Covers 67 bolted to the manifold give access to openings through which individual jet members 65 may be inspected. It has been found that to obtain satisfactory mixing of the gas and air, the gas must be conducted close to one of the regenerative masses and released in a small stream of high velocity. The heated air should leave the upstream mass at a velocity of approximately f.p.s. and a temperature of about 1800" F. In order to get good mixing, the velocity of the fuel gas leaving the nozzle should be at sonic velocity which requires that the pressure in the gas manifolds should be atmospheric pressure or higher when the furnace operates at l5" of vacuum.

The piping system `for the fuel nozzles 65 is shown in Figs. X and XI. Fuel under pressure is delivered to two valves 71 and 72 from a fuel supply pipe 70. One valve 71 feeds furnace 1 and valve 72 feeds furnace 2 (not -quickly establishes a proper distribution of heat.

shown). From the valves 71 and 72 thegas passes to two three-way valves 73, only one of which is shown in Fig. X since the Ifuel distribution is shown only for furnace 1 in that figure. This three-way valve 73 may be turned to either feed an upper series 74 of nozzles (as seen in Fig. X) ora lower series 75, each series consisting of ten nozzles 65, five on one side and ve on the other side of the furnace. The upper series of nozzles 74 feeds spaces 50 and 51 adjacent to the masses 32, 33 and 34 and the lower series feeds the spaces 50 and 51 adjacent to the masses 35, 36 and 37. Y

Figs. XII and XIII show two elevations of the main piping actually used in the cyclic operation of theprocess and Fig. XIV shows diagrammatically the same apparatus. This main piping includes pipes 80, 81, 82 and 83 connected as shown in Fig. XIV.

The apparatus operates on a preliminary heating step used only after the furnace has been standing inoperative for at least several hours. This preliminary heating step is followed by a repetitive cycle consisting of four steps which, yfor convenience, we will call steps A, B, C and D.

The preheating step is quite independent of the cyclic operation and uses only the apparatus shown in Fig. XV, each furnace being heated independently of the other. It is important that the furnaces be heated slowly and evenly by carefully controlled combustion produced in the furnace by the burners 12. The only regenerative material which I now consider suitable is ceramic; that is, it is produced by the firing of a suitable material in a kiln or the like. Such material can be injured by too rapid heating or cooling when used in the process herein described. Therefore, the preheating is produced by feeding a suita-ble `fuel oil or gas to the burners 12, the combustion being controlled to produce as complete a combustion as possible. The combustion mixture is fed from the burners 12 into the central combustion space 41 between the masses 34 and 35. The hot products of combustion flow slowly through all the channels of all masses into the extensions 30 and escape at a pressure slightly above atmospheric through the pipes 15, the valves 16 being open. The pumps 9 and 10 are not operating during the preheating step and there is no draft pulling these products of combustion into the main piping. The preheating step should be continued until the masses 34 and 35 of each furnace are at a temperature of 1500 F., or above. It is highly desirable that during preheating no free oxygen is introduced into the main piping to ,avoid later explosions during cyclic operation. When the furnace is sufficiently heated, the valves 16 are tightly vclosed and the valves 14 and 13 feeding fuel and air to the burners 12 are also tightly closed. The distribution of heat in the regenerative masses at the end of the pre- ,heating step lmay not be that desired yfor maximum production during cyclic operation, but the cyclic operation After the valves above designated are closed, the pumps 9 and .10 are started, thus establishing a vacuum inside the furnaces 1 and 2 and starting cyclic operation.

In starting the cyclic operation, which may continue rford-ays at a time, it is not important which of the steps A, B, C or D is started iirst. At the time of starting the cyclic operation, the heat in the furnaces due to preheatving may not be distributed exactly enough to give the best operation but in a very short time the cyclic operation will insure proper distribution of heat. During `cyclic operation one furnace is producing an off-gas con- The operation during the A step, as illustrated in Fig. .XVL is as follows:

Furnace 2 is operating on a heat step, cold air being -delivered through valves 6 and 7 and pipe 82 to an extension 30 of the furnace 2, which is shown in Figs. I and II. This cold air is heated in mass' 32 Vto a temperature, preferably above the ignition temperature'ofVV the fuel delivered through nozzles 65 to the spaces 50 andr51 ad7 jacent to the mass 33. A rapid and complete ccsmbusf` tion should occur and hot gases of combustion should pass to land through the mass 37 into the extension 30,

and through the pipe 83 and valves 7 and '8 and the pump 10 to the stack 11; During this operation, the mass 32 is cooled and masses 33, 34, 35 and 36 are heated. The hot products of combustion are cooled in the mass 37 and a substantial proportion of theheatrof the products of combustion is stored in the mass 37 and thereby saved for future use. Y Y 1- At the same time that the furnace 2 is being heated in a heat step, in operation A the furnace 1 is producing an off-gas containing a substantial proportion of acetylene in a make step, which operates as follows; At `the beginning of the make step in operation A, the mass 37 is substantially hotter than mass V32 since it has been heated in a previous heat step. Sufficient heat has then been stored in the masses 33, 34, 35 and 36 to heat the cold in-gas up to a reaction temperature and tofurther supply the necessary heat to -produce the desired off-gas by the endothermic reaction to acetylene.

Referring again to Fig. XVI, during the make step in operation A, and, in fact, in any make step, an'in-gas is prepared by mixingfa feed` gas, or a recycle gas, both containing a suitable hydrocarbon, or bothsuch `feed and recycle gases, in varying proportions', withadiluent, preferably steam. This in-gas is delivered through valves 8 and 5 andthe pipe 81 toan extension 30ffof furnace 1 and to the masses 37, 36, 35, 34, 33 and 32 to an extension 30 of the furnace 1, pipey 80, and through the valves 5 and 6 to the pump 9 which delivers an off@ gas containing a substantial proportion of acetylene. In its passage through the masses 'of furnace 1, the ingas is rst heated to a reaction temperature and heat is then supplied, from the masses 36 to33, 'inclusive,;sui cient to produce the desired reaction of the in-gas to the off-gas. The off-gas is then cooled by the relatively cold mass 32. During the entire cyclic process, the interior of yboth Vfurnaces is maintained at -a vacuumof about 15 inches of mercury. 'f

In steps B, C and D the make `and heat steps also occur simultaneously, the heat step oc'curring'in one furnace while the make -step occurs in the other. `The valves 6 and 8 are so connected lor interlocked that air cannot ever be mixed with iin-gas or olf-gas. In operation B, shown in Fig. XVII, V in-'gas 'is fed through valves 8 and 7 and pipe 83 into the furnace 2in which an off-gas is `formed in a make step, this off-gas being withdrawn through pipe 82 and valves 7 and 6 by the pump 9. At the same time furnace 1 is bein'g subjected :to a heat step by fuel supplied by fuel system 3 to the spaces Si) and 51 adjacent -to the mass 36, hot air being supplied to this space 5t) through the -mas's 37, the pipe S1 and the valves 5 and 6. i In operation C, as shown in Fig. XVIII, acetylene is making in the furnace 1 while furnace 2 isheating and in Fig. lXIX furnace 1 is heating and furnace 2 is making. The heat step and the make step are each separately controlledk in each furnace. '-Two` separate exhaust pumps are provided, the treated oif-gas'frorn each make step being always pulled' out of fthe-furnaces by the pump 9 and the cooled gases vof combustion from the heat step being always pulled out of the furnace by the pump 10. The characteristics ofeach pump may be suited to the service 'which they render. The pressure at which the gases enter thefurnaces. Vis also separately controlled by pressure regulating valves. Valve 91, which is in the pipe to valve 6, Vthrottles the air 4admitted to each furnace during its heat step to pro duce the required vacuum. Valve 92 controls the pres,- sure of fuel admitted to furnace 1 ,and valve 9,3 admits fuel t0 furnace 2.- YBy cgafrgllaathelspsed Qi Ramal() 7 and the valves 91, 92 and 93, the degree of vacuum and combustion in each furnace may be controlled. Similarly, the vacuum and temperature in each furnace may be controlled by the valve 94 and the pump 9. The pressure regulating valves 91, 92, 93 and 94 `are usually set during cyclic operation and once set are not disturbed. It is most important that separate controls be established on each furnace so that maximum operating efliciencies can be established in both the heat and make steps. The valves 6 and 8 being mechanicmly connected to turn together, neither air nor combustion gases can get into the off-gas and propane cannot be wasted in the stack 11. The partial pressure on the suitable hydrocarbon is, of course, lower than the pressure on the mixed gases, due to this mixture and to the presence of the diluent. These particulars are more pertinent to a process which will be described and claimed in a separate application therefor, but it should be borne in mind that the apparatus has no real utility unless it produces acetylene below a very dinitely xed and maintained cost per pound of acetylene. This cost and the corresponding market prices at which acetylene can be bought in cylinders or bulk or produced by calcium carbide are a direct function of the cost of producing calcium carbide from which practically all acetylene now used in the United States is produced. It is very easy to produce acetylene from suitable hydrocarbons, particularly petroleum gases or gases containing suitable hydrocarbons, but it is difficult even where low cost suitable gases are available fas charging stocks to produce acetylene at a cost competitive with hydrocarbons. I have found that to produce acetylene from any suitable hydrocarbon which I have found available in an apparatus such as has been previously described, the apparatus must have certain characteristics which will now be disclosed.

It is highly desirable that the furnaces be designed and equipped to process in-gases containing various suitable hydrocarbons in various proportions. The arrangement of regenerative masses shown in Figs. I and II make the furnaces adaptable to handling such variables in gases.

It should be noted that a separate set of fuel injection nozzles is provided at each side of the center of the furnace. The temperature gradient along the line of ow of gas being cracked is very important to the efficiency of the operation. Each of the sets of fuel injection nozzles is provided with a throttle valve to control the distribution of gas to each bank of fuel jets. Having once established the ow distribution desired, then the orifice size of the fuel injection nozzles may be altered to establish this same ow ratio with the throttle valves open.

To better describe these temperature profile control features, Fig. XX shows the temperature prole with all jets of equal size and with both throttle valves open. Under this condition, the amount of fuel in each of the two injection points Will be equal. This method of feeding the fuel gas will make a very smooth prole with a broad peak, as shown. It should be noted that the zone at high temperature is thus spread and the contact time at high temperature is increased.

If the throttle valves in the outer set of fuel jets is closed off land the same total amount of fuel is added through the jets nearest the middle of the furnace, the results shown in Fig. XXI will be obtained. It should be noted in this case that the maximum temperature is higher and that the peak is much sharper. This arrangement, therefore, will subject the gas being cracked to a higher temperature but for a shorter length of time. This is advantageous with some feed stocks, particularly where a single component material is supplied, such as propane or ethane, as compared with natural gas which is a mixture of hydrocarbon gases, each having different reacting characteristics. In this case, the temperature and time factors may be controlled to give the highest yield for the particular feed stock used.

Fig. XXII illustrates the temperature profile obtained with all of the fuel fed to the outer bank of jets. In this case, two peaks will be formed, as shown, the amount of drop-off of temperature depending upon the amount and nature of the feed stock. Since heat is being absorbed as the reaction takes place and acetylene is formed, heat is removed from the center section and the temperature will be substantially lowered.

If both sets of jets are used and the amount of fuel properly adjusted, the heat input and the heat absorbed may be equalized to give a temperature profile shown in Fig. XXIII.

This is advantageous with mixed feed as it is desirable to hold the gas at a predetermined temperature for a certain time with both of these factors under definite control.

It will thus be seen that the previously described arrangement of regenerative masses and fuel nozzles in the furnace assemblies is available for processing various suitable hydrocarbons.

The preceding description assumes that the hydrocarbon used as feed stock is a gas at atmospheric temperature and pressure. If it is desired to produce acetylene or ethylene by the process or in the apparatus previously described from a hydrocarbon which is a liquid at atmospheric temperature and pressure, certain additional apparatus and a different method become necessary. The gas delivered to the furnace must then contain a hydrocarbon gas or vapor, produced from a liquid hydrocarbon such as gas oil or the like. The gas so delivered should also contain a substantial proportion of steam.

The necessary apparatus for using a liquid hydrocarbon as a raw material in the furnace is shown in Figs. XXIV, XXV, and XXVI and includes a conventional type of boiler 101, a superheater 102, a mixer 103 and a valve 104.

Water is delivered to the boiler 101 through a pipe 105 and fuel is delivered to the boiler 101 through a pipe 106. Saturated steam is delivered to the superheater 102 through a pipe 107 and superheated steam is delivered from the superheater 102 through a pipe 108 to the mixer 103. The liquid hydrocarbon, for convenience called oil, may be delivered to the valve `104 through a pipe 109 and through valve 104 and a pipe 110 to the mixer `103.

It is sometimes desirable to so equip the plant that either oil or a gas such as propane may be supplied through a pipe 119 to the valve 104 and from the valve through a pipe 111 to the mixer 103.

Regardless of whether gas or oil is used in the operation of the plant, a gaseous mixture of hydrocarbon gas and steam is delivered through a pipe 112 to the valve 8 at the furnace. The ow of gas into the mixer 103 is controlled by an automatic regulator 113, the flow of oil in liquid form into the mixer 103 is controlled by an automatic regulator 114, and the flow of steam into the mixer 103 is controlled by the automatic regulator 115. Each of these regulators may be set manually to control the ow of a fluid therethrough within reasonable limits of, for example, within 5%, plus or minus, an established mean.

A satisfactory form of mixer is shown in Figs. XXV and XXVI. It consists of a body in which is threaded a shell 12'1. Between the end of the shell 121 and the lbody 120 is a diaphragm member 122 having a constricted orice 123, the diaphragm member 122 dividing the interior of the mixer into a steam chamber 124 and a mixing chamber 125. When gas is used through the pipe 111, it is mixed with steam delivered to the steam chamber '124 through the pipe 115 and delivered to the mixing chamber 125 through the orifice 123. A liquid hydrocarbon or oil is delivered to mixing chamber 125 through the pipe 110 whenever the valve 104 is turned to Celiver oil.

If the suitable hydrocarbon is a gas at atmospheric pressure, saturated steam may be used as a diluent, but, if any substantial fraction of the hydrocarbon so used has a boiling point substantially above the temperature ofsaturated steam at ordinary boiler pressures, such pressures would not vaporize all such fractions and superheated steam must be used.

When operating on a liquid hydrocarbon delivered by the pipe 109, the steam performs a double function. It furnishes the heat to vaporize the hydrocarbon and it acts as a diluent to reduce the partial pressure of the hydrocarbon in the in-gas delivered to the furnace through the valve 8 and thus reduces the temperature required to fully vaporize the liquid. It may also act to maintain the in-gas at a high temperature as it enters the reaction zone. However, the heat efficiency of superheaters of practical size is rather low and I prefer to use fuel in the furnaces rather than in the superheater.A

I prefer to maintain a vacuum of about 15 inches of mercury in the furnace, lbut this vacuum may vary considerably, and still result in a substantial production of the desired gas or gases provided that the combined effect of vacuum and steam is suicient to result in a low partial pressure of feed stock. The pressure found to be satisfactory is about inches of mercury for a C1 feed and proportionately less as the carbon is increased. For propane or other C3 `gases the pressure should be two inches, butane, 11/2", etc. The steam should be sufficiently superheated to maintain it at least slightly superheated in the in-gas passing through the valve 8. A higher superheat may result in a somewhat better economy, but a very high superheat may result in operational difficulties or a lower efficiency.

I claim as my invention:

l. A furnace adapted to form an off-gas containing a desired hydrocarbon by the pyrolysis of a suitable hydrocarbon, comprising:

a gas-tight metal shell;

a heat refractory lining in said shell;

two main regenerative masses separated by a central space and so placed as to leave an end space at each end of the furnace;

three auxiliary regenerative masses placed in said central space, all of the regenerative masses being so placed that passages through said masses provide open paths from one end of the furnace to the other end, said auxiliary masses being spaced apart an.1 spaced from said main masses to divide said central space into four subspaces separated by said auxiliary masses;

four series of fuel feeding nozzles in said furnace, each series of nozzles feeding fuel `into one of said subspaces;

valve means for feeding fuel through each of said nozzles, and adapted to feed fuel in substantially equal amounts through all of said nozzles, or in substantially equal amounts only to the two innermost subspaces, or in substantially equal amounts only to the two outermost subspaces, or in substantially equal amounts to the outermost of said subspaces and in reduced amounts to the innermost of said subspaces; and

air valve means for feeding air into each of said end spaces, said means being so placed and operated that air is fed into each end space whenever fuel is being fed into that end of said central space.

2. A furnace adapted to form an olf-gas containing a desired hydrocarbon by the pyrolysis of a suitable hydrocarbon, including:

a gas-tight metal shell;

a heat refractory lining in said shell;

two main regenerative masses separated by a central space and so placed as to leave Ian end space at each end of Ithe furnace;

first, second, and third auxiliary regenerative masses placed in said central space, all of said masses having 10 longitudinal passages therethroughy to provide open paths from one end of the furnace to the other end, said auxiliary masses being spaced apart and spaced from said main masses; Y Y

a first nozzle means communicating with said central space between one of said main masses and said first auxiliary mass for feeding fuel thereto;

a second nozzle means communicating with said central space between said first and second auxiliary masses for feeding fuel thereto;

a third nozzle means communicating with said central space between said second and mthird 4auxiliary masses for feeding fuel thereto;

a fourth nozzle means communicating with said central space between said third auxiliary mass and the other of said main masses for feeding fuel thereto;

means for selectively feeding fuel through said nozzl means; Y

means for alternatively feeding air into said end spaces; and

means for selectively throttling the flow of fuel through said nozzle means to vary the temperature -prole curve from end-to-end of the furnace.

3. A furnace adapted to form an offgas containing a desired hydrocarbon ,by the pyrolysis of a suitable hydrocarbon, including:

a gas-tight metal shell;

a heat refractory lining in said shell;

two main regenerative masses separated by a central space and so placed as to leave an end sp-ace at each end of .the furnace;

first, second, third, and fourth auxiliary masses placed in said central space, all of said masses having longitudinal passages therethrough to provide open paths from one end of the furnace to the other end, said auxiliary masses being spaced apart and spaced said main masses;

a first Inozzle means communicating with said central space .between one of said main masses and said first -auxiliary mass for feeding fuel thereto;

a second nozzle means communicating with said central space between said first and second auxiliary masses for feeding fuel thereto;

burner means communicating with said central space between said second and third auxiliary masses;

a thi-rd nozzle means communicating with said central space between said .third and fourth auxiliary masses for feeding fuel thereto;

a fourth nozzle means communicating with said central space between said fourth auxiliary mass and the other of said main masses for feeding fuel thereto;

means for selectively feeding fuel through said nozzle means; means for selectively throttling the flow of fuel through said nozzle means to vary the temperature profile curve from end-to-end of the furnace;

means for feeding a heating mixture through said burner means; and

means for alternatively feeding air into said end spaces.

4. In a furnace installation for the pyrolysis of hydrocarbons, the combination of:

first and second regenerative furnaces, each having a -gasatight metal shell, a heat refractory lining in said shell, two main regenerative masses in said lining and separated by a central space and so placed as to leave first and second end spaces at the ends of the furnace, a central regenerative mass in said space and between said main masses, and series of fuel feeding nozzles in the furnace communicating with said central space;

first connecting means for alternatively connecting said source of in-gas with the first or second spaces of both of said furnaces;

second connecting means for alternatively connecting said source of air with the first or second end spaces of both of said furnaces;

third connecting means for alternatively connecting saidsource of fuel with the'central spaces of said diurnaces;

fourth connecting means for nalternatively connecting said point of gas storage with the first or second end spaces of both of said furnaces;

`fifth connecting means for alternatively connecting said point of lgas discharge with 4the first or second end spaces of both of said furnaces;

means for continuously feeding in-gas through said rst connecting means, in a first step, to the second end space of said second furnace, then in a second step to the second end space of said first furnace, then in a third step to the first end space of said second furnace, and then in a fourth step to the first end space of said iirst furnace;

means :for continuously drawing ofi cracked gas through said fourth connecting means to the point of gas storage, in said first step from .the first end space of said second furnace, in said second step from the rst end space of said first furnace, in said third step from the second e'nd space of said second furnace, and in said fourth step from the second end space of said first furnace;

means for continuously feeding fuel through said third connecting means from said source of fuel, in said rst References Cited in the file of this patent UNITED STATES PATENTS 1,691,300 Ormont Nov. 13, 1928 1,944,483 Zieley Jan. 23, 1934 2,185,566 Porter et al. Ian. 2, 1940 2,209,973 Houdry Vet a1. Aug. 6, 1940 2,218,495 Balcar Oct. 15, 1940 2,309,137 Peterkin Jan. 26, 1943 2,556,835 Bair June 12, 1951 2,692,819 Hasche et al. Oct. 26, 1954 2,718,534 Harris Sept. 20, 1955 2,785,212 Begley Mar. 12, 1957 

1. A FURNACE ADAPTED TO FORM AN OF-GAS CONTAINING A DESIRED HYDROCARBON BY THE PYROLYSIS OF A SUITABLE HYDROCARBON, COMPRISING: A GAS-TIGHT METAL SHELL, A HEAT REFRACTORY LINING IN SAID SHELL, TWO MAIN REGENERATIVE MASSES SEPARATED BY A CENTRAL SPACE AND SO PLACED AS TO LEAVE AN END SPACE AT EACH END OF THE FURNACE, THREE AUXILIARY REGENERATIVE MASSES PLACED IN SAID CENTRAL SPACE, ALL OF THE REGENERATIVE MASSES BEING SO PLACED THAT PASSAGES THROUGH SAID MASSES PROVIDE OPEN PATHS FROM ONE END OF THE FURNACE TO THE OTHER END, SAID AUXILIARY MASSES BEING SPACED APART AN 1 SPACED FROM SAID MAIN MASSES TO DIVIDE SAID CENTRAL SPACE INTO FOUR SUBSPACES SEPARATED BY SAID AUXILIARY MASSES, FOUR SERIES OF FUEL FEEDING NOZZLES IN SAID FURNACE, EACH SERIES OF NOZZLES FEEDING FUEL INTO ONE OF SAID SUBSPACES, VALVE MEANS FOR FEEDING FUEL THROUGH EACH OF SAID NOZZLES, AND ADAPTED TO FEED FUEL IN SUBSTANTIALLY EQUAL AMOUNTS THROUGH ALL OF SAID NOZZLES, OR IN SUBSTANTIALLY EQUAL AMOUNTS ONLY TO THE TWO INNERMOST SUBSPACES, OR IN SUBSTANTIALLY EQUAL AMOUNTS ONLY TO THE TWO OUTERMOST SUBSPACES, OR IN SUBSTANTIALLY EQUAL AMOUNTS TO THE OUTERMOST OF SAID SUBSPACES AND IN REDUCED AMOUNTS TO THE INNERMOST OF SAID SUBSPACES, AND AIR VALVE MEANS FOR FEEDING AIR INTO EACH OF SAID END SPACES, SAID MEANS BEING SO PLACED AND OPERATED THAT AIR IS FED INTO EACH END SPACE WHENEVER FUEL IS BEING FED INTO THAT END OF SAID CENTRAL SPACE. 